A tandem-type color laser printer is well known in the art as a type of electrophotographic color printer. The tandem-type color laser printer has a plurality of photosensitive drums juxtaposed in a prescribed direction and provided one for each of the toner colors yellow, magenta, cyan, and black, and a plurality of developer cartridges respectively corresponding to the photosensitive drums for supplying toner to the photosensitive drums.
One type of tandem-type color laser printer includes a main casing, a drum unit detachably provided in the main casing and provided with the photosensitive drums, and the developer cartridges provided with developing rollers and detachably mounted in the drum unit. In the color laser printer, bosses are provided on each developer cartridge, and pressing members are provided in the drum unit for pressing the bosses provided on the developer cartridge.
In order to mount the developer cartridge in the drum unit, the developer cartridge is pushed downward into the drum unit until the developing roller held in the developer cartridge contacts the corresponding photosensitive drum in the drum unit so that the developer cartridge is positioned at a detached position. Next, the developer cartridge is tilted forward so that the bosses on the developer cartridge slide underneath the pressing members and the developer cartridge is positioned at an image-forming position. At this time, the pressing members suppress the bosses, pressing the developing roller to the photosensitive drum, thereby completing the operation for mounting the developer cartridge in the drum unit.